The air we breathe can contain pollutants called Particulate Matter (PM), measured in microns. A human hair measures around 100 microns. Inhalable particles under 10 microns in diameter, such as pollen, are known as PM 10, while cooking gases and other pollutants can be PM 2.5 or less. Because our houses tend to be more sealed these days, pollutants and allergens can't always escape. But they can be captured.